The present invention relates to a spark plug for an internal combustion engine.
In general, a spark plug includes a metal housing having a fixing screw portion provided on an outer surface thereof so as to be installed to an engine via this fixing screw portion. An insulator, fixed in the metal housing, has one end portion protruding from one end portion of the metal housing. A center electrode, fixed in an axial hole of the insulator, has one end portion protruding from one end portion of the insulator. A ground electrode has one end portion fixed to the metal housing, a bent portion provided at an intermediate portion thereof, and the other end portion positioned in a confronting relationship with one end portion of the center electrode to form a spark discharge gap.
For example, the Japanese patent application laid-open No. 2002-343533 corresponding to the U.S. Pat. No. 6,794,803 discloses a conventional spark plug capable of securing good heat-resisting properties of a ground electrode based on improvement in the relationship between a surface area and a volume of this ground electrode.
Recent advanced engines are generally required to have low fuel consumption and high power output. To assure stable ignition with lean fuel mixture, the flow velocity of fuel mixture tends to be increased at a spark discharging portion of the spark plug.